Thallium elimination

The competitive replacement Tl /K creates an interesting toxicokinetic factor in terms of thallium elimination, namely direct active excretion into the intestinal lumen. In contrast to other toxic heavy metals, fecal elimination of thallium is the predominant route of excretion. In addition to thallium possibly binding in the gastrointestinal tract in cases of acute intoxication (cf. Section 22.6.2), reabsorption may occur by the enterohepatic and enterosystemic circulations, thereby prolonging the biological half-life. In fact, half-lives of between 3 and... 

Selectivity of propylene oxide from propylene has been reported as high as 97% (222). Use of a gas cathode where oxygen is the gas, reduces required voltage and eliminates the formation of hydrogen (223). Addition of carbonate and bicarbonate salts to the electrolyte enhances ceU performance and product selectivity (224). Reference 225 shows that use of alternating current results in reduced current efficiencies, especiaHy as the frequency is increased. Electrochemical epoxidation of propylene is also accompHshed by using anolyte-containing silver—pyridine complexes (226) or thallium acetate complexes (227,228). 

A variety of therapies for thallium poisoning have been suggested by neutralising thallium in the intestinal tract, hastening excretion after resorption, or decreasing absorption. Berlin-Blue (fertihexacyanate) and sodium iodide in a 1 wt % solution have been recommended. Forced diuresis hemoperfusion and hemodialysis in combination results in the elimination of up to 40% of the resorbed thaHous sulfate (39). 

The recently reported (757) conversion of 5-pyrazolones directly to a,j8-acetylenic esters by treatment with TTN in methanol appears to be an example of thallation of a heterocyclic enamine the suggested mechanism involves initial electrophilic thallation of the 3-pyrazolin-5-one tautomer of the 5-pyrazolone to give an intermediate organothallium compound which undergoes a subsequent oxidation by a second equivalent of TTN to give a diazacyclopentadienone. Solvolysis by methanol, with concomitant elimination of nitrogen and thallium(I), yields the a,)S-acetylenic ester in excellent (78-95%) yield (Scheme 35). Since 5-pyrazolones may be prepared in quantitative yield by the reaction of /3-keto esters with hydrazine (168), this conversion represents in a formal sense the dehydration of /3-keto esters. In fact, the direct conversion of /3-keto esters to a,jS-acetylenic esters without isolation of the intermediate 5-pyrazolones can be achieved by treatment in methanol solution first with hydrazine and then with TTN. 

The thallium trinitrate-mediated ring contraction of frani-decal-2-ones has opened up a new route to the hydrindane system, and fluorinative ring contraction of cyclic alkenes to afford difluorocycloalkanes has been induced by iodotoluene difluoride and EtsN-HF. A possible mechanism is shown in Scheme 78. The double bond of the cyclohexene ring is attacked by iodotoluene difluoride activated by HF from the axial direction, followed by the addition of a fluoride ion from the trans direction. Reductive elimination of iodotoluene from the resulting adduct, ring contraction and the addition of the fluoride ion to the carbocation stabilized by fluorine then take place to give the ring-contracted difluorinated product. 

A clean twofold Heck coupling of unsubstituted butadiene 46 (R = H) in the 1- and 4-positions has not been reported. However, the initial carbopalladation product from 46 (R = H) and an in situ formed arylpalladium halide, the cr-allylpalladium halide 47 equilibrating with the corresponding 7r-allylpalladium halide, can efficiently be trapped with the anion formed by arylation of malononitrile or cyanoacetate to give 48, a product of reductive 1,4-arylation-alkylation of 1,3-butadiene 46 (R = H)." /3-Hydride elimination from the intermediate 47 (R H) can be accomplished when the reaction is carried out in the presence of silver acetate or thallium acetate, leading to the... 

An intEiesting variant on the Wilgerodt reaction offers a simple three-step procedure that avoids the wastage involved in the schemes above, which require the incorporation of an extra carbon atom that must later be eliminated. The sequence starts with the acylation of isobutylbenzene (49-1) with propionyl chloride to give propiophenone (49-2). Reaction of that with thallium 111 nitrate and methyl ortho-formate in methanol leads in high yield to the methyl ester (49-3) of ibuprofen [50]. This would be the method of choice for preparing the dmg but for two unfortunate facts the extreme toxicity of thallium and the very high sensitivity of analytical methods for the detection of metals. It proved to be virtually impossible, in practice, to produce samples that showed zero residues of thallium. 

The treatment of thallium poisoning is rather ingenious. It takes three forms diuretics eliminate thallium through increased urine production Prussian blue dye traps thallium excreted into the gut, preventing its reabsorption and potassium chloride supplements displace the thallium that has already been absorbed into the tissues. These measures allowed the unfortunate child from Qatar to make a complete recovery. 

Final proof for the inferred structure (1) for cyclosporin A and a first insight in the shape of the molecule resulted from X-ray analysis and high-resolution NMR spectra. The preparation of a crystallized derivative containing a heavy atom was achieved by an addition reaction using iodine and thallium(I) acetate. Instead of the expected iodoacetoxy derivative, the cyclic product (11) was obtained. Obviously, the reaction proceeded by a selective addition of iodine to the double bond of the MeBmt unit followed by an internal cyclization with the participation of the OH group. Iodocyclosporin A (11) reverted easily with Zn powder in acetic acid into genuine cyclosporin A by rranr-elimination. X-ray analysis [6] revealed that iodocyclosporin A assumes a rather rigid backbone conformation. The amino acids 1-6 adopt an antiparallel, markedly twisted /i-pleated sheet conformation, whereas the residues 7-11 form a loop. 

In the reaction of allyl acetate 217 with ketene silyl acetal 218 of methyl acetate, using a Pd catalyst coordinated to DPPP, cyclopropane 220 is formed in addition to the expected allylacetate 219 [104], The cyclopropanation becomes main reaction when TMEDA, as a ligand, and thallium acetate are added [105]. The cyclopropanation can be understood by the attack of the enolate ion at the central carbon of 7r-allylpalladium to form the palladacyclobutane 221, followed by reductive elimination. 

To reach the low detection limits and eliminate the possibility of matrix interferences, choose the GFAA methods for analysis of antimony, arsenic, beryllium, cadmium, chromium, lead, selenium, silver, and thallium. 

Heck intramolecular cyclization. Silver carbonate or nitrate was added originally to tandem Heck arylation reactions to depress alkene isomerization, but they also improve selectivity in the -elimination step. Grigg et al.1 have used a number of useful additives such as triethylammonium chloride, sodium formate (15, 248), phenylzinc chloride, as well as silver(l) and thallium(I) salts. In fact, thallium(I) salts... 

Pyrazolylborates, whose steric demands can be readily altered by substitution, have been studied both structurally and by solvent extraction procedures. The compound [rj3-HB(3-Bu pz)3]BeMe was made by interaction of the thallium salt of HTp and (BeMe2) with elimination of TIMe it has the structure shown in (4-III).6... 

Elimination of Tl is mainly through the gastrointestinal tract but elimination also occurs through the kidneys, saliva, hair, skin, sweat, and breast milk. Relative amounts excreted by each route vary by species. Thallium is likely excreted through intestinal and gastric secretions associated with potassium loss or excretion. Likewise, reabsorption of Tl also occurs, mainly from the colon. The estimated biological half-life of Tl is 10 days but values up to 1 month have been reported (WHO, 1996). 

Thalliuin(III) trifluoroacetate will also eliminate trifluoroacetic acid in reactions with compounds containing N—H bonds 40, 240). Thus, brief treatment of octaethylporphyrin in CHgCla and tetrahydrofuran with an excess of T1(02CCF3)3 followed by chromatography on deactivated alumina affords the complex shown in Fig. 10, This was the first unambiguous characterization of a thallium(III) porphyrin 240). 

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